The elucidation of the structure of compounds derived from plant and animal sources is an integral component of the search for new chemotherapeutic agents. In a widely practiced approach to structure elucidation, the chemist examines the chemical and spectroscopic properties of the intact molecule, its simple derivatives, and possibly one or more of its degradation products. The unit process can be described as a stepwise sequence of experiment design (chemical or spectroscopic), data collection, and reduction of data to its structural implications, i.e., a partial structure. This unit process is recycled until expansion of the partial structure into a completely defined molecular expression is achieved. By incorporating the high-speed computer, an already proven method of structure elucidation can be transformed into a more efficient, more error-free version. Existing software (Program CASE - Computer-Aided Structure Elucidation) can expand a partial structure at any stage in the structure elucidation problem into all molecular expressions consistent with it, and any other structural constraints imposed by the available data. An examination of the computer-generated structures affords an invaluable guide in the design of new experiments to correctly identify the unknown structure with a minimum input of time and effort. At the last stages of the problem the computer can assure the chemist that one or more structures equally consistent with the evidence were not overlooked.